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四(si)川盆地聚居(ju)著(zhu)四(si)川省和重慶(qing)市大部分人(ren)口、居(ju)民主要為(wei)漢(han)族巴蜀民系。是中國(guo)和世界上(shang)人(ren)口最多的區(qu)域之一。
中國(guo)著名紅層盆(pen)地(di)(di)，中國(guo)各大盆(pen)地(di)(di)中形態最(zui)(zui)典型、緯度最(zui)(zui)南、海(hai)(hai)拔(ba)最(zui)(zui)低的盆(pen)地(di)(di)。位于(yu)長江上游(you)地(di)(di)區(qu)，海(hai)(hai)拔(ba)500米左右，長江把它和東海(hai)(hai)一(yi)脈相連(lian)，它是中國(guo)最(zui)(zui)大的外流盆(pen)地(di)(di)。
四川(chuan)盆(pen)(pen)地(di)(di)的(de)(de)(de)(de)面(mian)(mian)(mian)積(ji)(ji)約26萬(wan)余平方千米（面(mian)(mian)(mian)積(ji)(ji)是(shi)居第(di)五(wu)第(di)六位的(de)(de)(de)(de)兩湖盆(pen)(pen)地(di)(di)和銀額盆(pen)(pen)地(di)(di)的(de)(de)(de)(de)兩倍(bei)），占四川(chuan)省(sheng)面(mian)(mian)(mian)積(ji)(ji)的(de)(de)(de)(de)46%。四川(chuan)盆(pen)(pen)地(di)(di)西(xi)依青藏高原(yuan)(yuan)和橫(heng)斷山(shan)(shan)脈，北(bei)(bei)近秦巴(ba)山(shan)(shan)脈，與漢(han)中盆(pen)(pen)地(di)(di)相望(wang)，東(dong)接湘(xiang)鄂(e)西(xi)山(shan)(shan)地(di)(di)，南(nan)(nan)連云貴高原(yuan)(yuan)，盆(pen)(pen)地(di)(di)北(bei)(bei)緣(yuan)(yuan)米倉山(shan)(shan)，南(nan)(nan)緣(yuan)(yuan)大婁(lou)山(shan)(shan)，東(dong)緣(yuan)(yuan)巫山(shan)(shan)，西(xi)緣(yuan)(yuan)邛崍山(shan)(shan)，西(xi)北(bei)(bei)邊緣(yuan)(yuan)龍門山(shan)(shan)，東(dong)北(bei)(bei)邊緣(yuan)(yuan)大巴(ba)山(shan)(shan)，西(xi)南(nan)(nan)邊緣(yuan)(yuan)大涼山(shan)(shan)，東(dong)南(nan)(nan)邊緣(yuan)(yuan)相望(wang)于(yu)武陵山(shan)(shan)。這(zhe)里的(de)(de)(de)(de)巖(yan)石，主要由(you)紫(zi)紅色砂巖(yan)和頁巖(yan)組(zu)成(cheng)。這(zhe)兩種巖(yan)石極(ji)易(yi)風化發育成(cheng)紫(zi)色土(tu)。紫(zi)色土(tu)含有豐富(fu)的(de)(de)(de)(de)鈣、磷、鉀等營養元素，是(shi)南(nan)(nan)方最肥(fei)沃的(de)(de)(de)(de)自然土(tu)壤。四川(chuan)盆(pen)(pen)地(di)(di)是(shi)全國紫(zi)色土(tu)分(fen)(fen)(fen)布(bu)最集中的(de)(de)(de)(de)地(di)(di)方，向(xiang)有“紫(zi)色盆(pen)(pen)地(di)(di)”的(de)(de)(de)(de)美稱。四川(chuan)盆(pen)(pen)地(di)(di)底(di)部面(mian)(mian)(mian)積(ji)(ji)約16萬(wan)多平方千米，按其地(di)(di)理(li)差異(yi)，自西(xi)向(xiang)東(dong)又可分(fen)(fen)(fen)為成(cheng)都(dou)平原(yuan)(yuan)、川(chuan)中丘陵和川(chuan)東(dong)平行嶺谷三部分(fen)(fen)(fen)。成(cheng)都(dou)平原(yuan)(yuan)西(xi)方是(shi)龍門山(shan)(shan)脈，東(dong)方是(shi)龍泉山(shan)(shan)脈。
四川盆(pen)地可(ke)明顯分為邊緣(yuan)山地和(he)盆(pen)地底部兩大(da)部分，其面積分別約(yue)為10萬(wan)多(duo)和(he)16多(duo)萬(wan)平(ping)方公里。邊緣(yuan)山地多(duo)中山和(he)低山。
景觀各要素過渡性明顯，如動植物(wu)組成上(shang)分別(bie)滲透了華(hua)中(zhong)區、西南區、青藏高(gao)原(yuan)區和華(hua)北(bei)區的(de)成分。邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)地(di)(di)區從下而(er)上(shang)一(yi)般具有2～5個垂直自然分帶。邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)地(di)(di)是四(si)川(chuan)多(duo)種(zhong)經(jing)濟林木(mu)和用材林基地(di)(di)。農(nong)業上(shang)水土流失較為嚴重(zhong)。盆地(di)(di)底部多(duo)丘陵、低山(shan)(shan)(shan)(shan)和平原(yuan)。地(di)(di)表組成物(wu)質(zhi)新而(er)單(dan)一(yi)，多(duo)砂泥巖(yan)與(yu)第四(si)紀沉(chen)積物(wu)。氣候上(shang)屬(shu)中(zhong)亞熱帶，熱量(liang)遠比邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)地(di)(di)為高(gao)，但降水量(liang)不及邊(bian)(bian)緣(yuan)(yuan)山(shan)(shan)(shan)(shan)地(di)(di)。植被為人工的(de)次生(sheng)林木(mu)所代替，覆被率低，耕地(di)(di)連片(pian)，夏伏旱和洪澇是這一(yi)地(di)(di)區最大災害。
盆地(di)內部地(di)形地(di)貌(mao)(mao)顯示出明顯的三分特點，即(ji)盆西(xi)平(ping)原地(di)貌(mao)(mao)、盆中丘陵地(di)貌(mao)(mao)和盆東山地(di)地(di)貌(mao)(mao)，三者(zhe)以(yi)龍泉(quan)山和華鎣山為界。
四川盆(pen)地(di)(di)(di)其(qi)輪廓形態總(zong)體(ti)近似(si)長(chang)方形，形似(si)信(xin)封(feng)狀，右(you)傾(qing)斜(xie)置在亞洲(zhou)大(da)陸，因此被地(di)(di)(di)理學者稱之(zhi)為(wei)信(xin)封(feng)盆(pen)地(di)(di)(di)。信(xin)封(feng)盆(pen)地(di)(di)(di)東(dong)部(bu)頂(ding)點(dian)云(yun)陽(yang)（靠近萬州(zhou)），南(nan)部(bu)頂(ding)點(dian)敘永(靠近遵義)，西(xi)部(bu)頂(ding)點(dian)雅(ya)安，北部(bu)頂(ding)點(dian)廣元。信(xin)封(feng)盆(pen)地(di)(di)(di)幾何中(zhong)心城市遂寧（幾何中(zhong)心點(dian)大(da)致(zhi)在蓬溪南(nan)部(bu)地(di)(di)(di)區），中(zhong)北部(bu)（內頂(ding)角）中(zhong)心城市南(nan)充，中(zhong)南(nan)部(bu)內頂(ding)角安岳。
四川盆地西部的成都和東(dong)南(nan)部的重慶皆為國家中心城(cheng)市。
四川盆(pen)(pen)地(di)由盆(pen)(pen)周山地(di)和盆(pen)(pen)地(di)底部構成(cheng)。
盆周東部為(wei)長江三(san)峽，南部為(wei)云貴(gui)高(gao)(gao)原，西部為(wei)青藏(zang)高(gao)(gao)原，北部為(wei)大巴山。
盆地底(di)部(bu)主(zhu)要(yao)分(fen)(fen)為(wei)川(chuan)東(dong)平行嶺(ling)谷、川(chuan)中(zhong)丘陵(ling)(ling)和(he)川(chuan)西成都(dou)(dou)平原(yuan)三(san)部(bu)分(fen)(fen)。龍泉(quan)山是成都(dou)(dou)平原(yuan)和(he)川(chuan)中(zhong)丘陵(ling)(ling)的(de)(de)界山，華鎣山是川(chuan)中(zhong)丘陵(ling)(ling)和(he)川(chuan)東(dong)平行嶺(ling)谷的(de)(de)界山。
（1）在龍(long)泉(quan)山(shan)和龍(long)門山(shan)、邛崍山(shan)之間的盆西(xi)平(ping)原，系斷裂下陷(xian)由岷江水(shui)系的河流沖(chong)積而成(cheng)，面(mian)積約8000平(ping)方千米(mi)，為我國西(xi)南最大(da)的平(ping)原，因成(cheng)都(dou)位于(yu)平(ping)原之中(zhong)， 故稱(cheng)成(cheng)都(dou)平(ping)原。成(cheng)都(dou)平(ping)原海拔460米(mi)～750米(mi)，地勢由西(xi)北向(xiang)東南傾斜，地表(biao)平(ping)坦，相對高(gao)差一般不超(chao)過(guo)30米(mi)～50米(mi)，它由岷江、沱江、涪江、青衣(yi)江等(deng)八(ba)條(tiao)河流沖(chong)積聯(lian)綴而成(cheng)，土(tu)壤肥沃(wo)，河渠稠密，有(you)著名(ming)的都(dou)江堰自(zi)流灌(guan)溉，自(zi)古(gu)以來素有(you)“天府”之稱(cheng)。
（2）在龍泉山(shan)和華鎣(ying)山(shan)之(zhi)間的(de)盆中丘(qiu)(qiu)陵，地勢(shi)低矮，海(hai)拔大多(duo)(duo)在300米(mi)～500米(mi)之(zhi)間，相對高(gao)差50米(mi)～150米(mi)，地勢(shi)由北(bei)向南(nan)傾(qing)斜(xie)，巖層近于水(shui)平(ping)，在流水(shui)的(de)長期侵(qin)蝕(shi)切割作用下，形成臺階(jie)狀的(de)方山(shan)丘(qiu)(qiu)陵，南(nan)部多(duo)(duo)淺(qian)丘(qiu)(qiu)，北(bei)部多(duo)(duo)深丘(qiu)(qiu)。丘(qiu)(qiu)陵地表軟(ruan)硬相間的(de)紫紅色砂、頁巖極易(yi)風(feng)化為紫色土，富含(han)磷鉀，自(zi)然肥力(li)較高(gao)，宜(yi)種性(xing)廣，是四(si)川全省糧食、經濟作物主(zhu)產(chan)區。
（3）華鎣(ying)山(shan)以(yi)東(dong)(dong)為盆(pen)東(dong)(dong)平行嶺(ling)(ling)谷(gu)區，由多條近東(dong)(dong)北西南走(zou)向(xiang)的條狀(zhuang)背斜山(shan)地(di)(di)(di)與向(xiang)斜寬谷(gu)組成，山(shan)地(di)(di)(di)陡而(er)窄，高700米(mi)-1000米(mi)，其(qi)中(zhong)，華鎣(ying)山(shan)高1705米(mi)，為盆(pen)地(di)(di)(di)底部最高峰(feng)。山(shan)地(di)(di)(di)頂部的石灰巖被雨水溶蝕后，常成凹槽(cao)(cao)，故山(shan)地(di)(di)(di)大多具(ju)有“一山(shan)二(er)嶺(ling)(ling)一槽(cao)(cao)”或(huo)“一山(shan)三(san)嶺(ling)(ling)二(er)槽(cao)(cao)”的特色。山(shan)嶺(ling)(ling)間的谷(gu)地(di)(di)(di)寬而(er)緩，海(hai)拔300米(mi)～500米(mi)，其(qi)間丘陵(ling)、平壩交(jiao)錯分布，是平行嶺(ling)(ling)谷(gu)區工農業(ye)生(sheng)產主要地(di)(di)(di)區。
四川盆地(di)邊緣山地(di)區屬強烈上升(sheng)的褶(zhe)皺帶(dai)。
地貌顯(xian)著特征是，海拔較(jiao)高(gao)(gao)，過渡性明(ming)顯(xian)，均為一(yi)系列中山(shan)(shan)和低(di)山(shan)(shan)所圍繞。盆地北緣(yuan)米(mi)(mi)(mi)倉(cang)山(shan)(shan)、大巴(ba)山(shan)(shan)近東西走(zou)向，是秦巴(ba)山(shan)(shan)地南翼部分，海拔一(yi)般在1500米(mi)(mi)(mi)～2200米(mi)(mi)(mi)之間，山(shan)(shan)勢(shi)雄偉(wei)，山(shan)(shan)坡陡峭，溝谷深切，相對(dui)高(gao)(gao)差(cha)可達500米(mi)(mi)(mi)～1000米(mi)(mi)(mi)；南緣(yuan)大婁山(shan)(shan)屬氣勢(shi)磅(bang)礴的云貴高(gao)(gao)原之一(yi)部分；西緣(yuan)有龍門山(shan)(shan)、邛(qiong)崍山(shan)(shan)、峨(e)(e)眉山(shan)(shan)，山(shan)(shan)脊海拔都在1500米(mi)(mi)(mi)至(zhi)～3000米(mi)(mi)(mi)以上，相對(dui)高(gao)(gao)差(cha)可達1000米(mi)(mi)(mi)，屬中國地勢(shi)第一(yi)級階(jie)梯。峨(e)(e)眉山(shan)(shan)頂峰高(gao)(gao)3099米(mi)(mi)(mi)，與附(fu)近的平(ping)原相對(dui)高(gao)(gao)差(cha)達2660米(mi)(mi)(mi)，山(shan)(shan)勢(shi)巍峨(e)(e)秀麗，為中國四大佛教名山(shan)(shan)之一(yi)。
四周為海拔2000～3000米(mi)的(de)(de)山(shan)(shan)脈和高原(yuan)所環繞，北(bei)面是(shi)大(da)巴(ba)山(shan)(shan)、米(mi)倉山(shan)(shan)、龍門山(shan)(shan)，西面是(shi)青藏(zang)高原(yuan)邊緣的(de)(de)邛崍山(shan)(shan)、大(da)涼山(shan)(shan)，南面是(shi)大(da)婁山(shan)(shan)，東面是(shi)巫山(shan)(shan)。
無論從(cong)構(gou)造還(huan)是(shi)人地(di)(di)(di)(di)貌(mao)上(shang)看，四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)都(dou)(dou)是(shi)一(yi)個(ge)典型(xing)的(de)(de)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)。它從(cong)震旦紀以來就是(shi)地(di)(di)(di)(di)殼比較穩定的(de)(de)大(da)(da)型(xing)拗陷(xian)區。晚三迭紀的(de)(de)印支(zhi)運(yun)動中(zhong)(zhong)(zhong)成(cheng)(cheng)(cheng)為(wei)一(yi)個(ge)內(nei)(nei)(nei)陸湖盆(pen)(pen)(pen)(pen)(pen)，但范圍(wei)要比今日的(de)(de)四(si)川(chuan)大(da)(da)得多(duo)(duo)，中(zhong)(zhong)(zhong)生代堆積(ji)了(le)厚達(da)3000～4000米(mi)的(de)(de)紫紅色(se)的(de)(de)砂巖和(he)頁巖，因此人們又(you)稱它為(wei)“紅色(se)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)”或(huo)“紫色(se)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)”。中(zhong)(zhong)(zhong)生代末期的(de)(de)四(si)川(chuan)運(yun)動使(shi)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)周圍(wei)褶皺成(cheng)(cheng)(cheng)山(shan)，中(zhong)(zhong)(zhong)間相(xiang)對(dui)下(xia)陷(xian)，輪廓基(ji)本形(xing)成(cheng)(cheng)(cheng)，盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)內(nei)(nei)(nei)部(bu)地(di)(di)(di)(di)層(ceng)也發生大(da)(da)規模的(de)(de)變(bian)形(xing)。東(dong)(dong)(dong)部(bu)出(chu)現一(yi)組北東(dong)(dong)(dong)向的(de)(de)褶皺，稱盆(pen)(pen)(pen)(pen)(pen)東(dong)(dong)(dong)褶皺帶(dai)；中(zhong)(zhong)(zhong)部(bu)形(xing)成(cheng)(cheng)(cheng)穹窿構(gou)造，稱盆(pen)(pen)(pen)(pen)(pen)中(zhong)(zhong)(zhong)穹窿帶(dai)；西部(bu)表(biao)現成(cheng)(cheng)(cheng)為(wei)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)沉陷(xian)帶(dai)，為(wei)今天盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)的(de)(de)三個(ge)地(di)(di)(di)(di)貌(mao)區奠定了(le)基(ji)礎。新(xin)生代的(de)(de)喜馬(ma)拉雅運(yun)動使(shi)周圍(wei)山(shan)地(di)(di)(di)(di)再次(ci)上(shang)升，盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)再次(ci)相(xiang)對(dui)下(xia)陷(xian)， 成(cheng)(cheng)(cheng)都(dou)(dou)一(yi)帶(dai)下(xia)陷(xian)更深。同時，長(chang)江(jiang)切穿巫山(shan)，滾滾東(dong)(dong)(dong)流，完(wan)成(cheng)(cheng)(cheng)了(le)統一(yi)的(de)(de)長(chang)江(jiang)水系，使(shi)內(nei)(nei)(nei)流盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)轉變(bian)為(wei)外流盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)。四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)可(ke)明(ming)顯分為(wei)邊緣山(shan)地(di)(di)(di)(di)和(he)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)底部(bu)兩大(da)(da)部(bu)分，其面(mian)積(ji)分別約為(wei)10萬多(duo)(duo)和(he)16萬多(duo)(duo)平方千米(mi)。 四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)是(shi)我國最大(da)(da)的(de)(de)外流盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)，面(mian)積(ji)26萬多(duo)(duo)平方千米(mi)。四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)(di)內(nei)(nei)(nei)部(bu)丘(qiu)陵(ling)、平原交錯，地(di)(di)(di)(di)勢北高南低。由于地(di)(di)(di)(di)表(biao)形(xing)態的(de)(de)不同，以華鎣山(shan)、龍泉山(shan)為(wei)界(jie)。
盆底可分為三部分：
①華鎣山(shan)(shan)以東為大致平行的川東嶺谷，由東北—西南走(zou)向的許多(duo)條狀山(shan)(shan)體組成，海拔一般(ban)在700～800米，谷地中(zhong)多(duo)低丘與平壩，海拔200～500米，是川東農業和人口集中(zhong)的地方。
②華鎣(ying)山(shan)和龍(long)泉山(shan)之間為方(fang)山(shan)丘陵(ling)(ling)，即川中丘陵(ling)(ling)。區(qu)內由于(yu)紫紅(hong)色砂頁巖傾角平(ping)緩，受切(qie)割(ge)后形成大(da)片方(fang)山(shan)式丘陵(ling)(ling)。海拔350～450米，相(xiang)對高(gao)度幾十(shi)米。當(dang)地勞動人民(min)利用方(fang)山(shan)山(shan)丘土層深厚(hou)的特(te)點(dian)，把梯田一直(zhi)修到(dao)山(shan)頂(ding)。
③龍泉山以西(xi)為(wei)平(ping)(ping)原(yuan)(yuan)。稱為(wei)川(chuan)西(xi)平(ping)(ping)原(yuan)(yuan)或成都平(ping)(ping)原(yuan)(yuan)，面積(ji)6000多平(ping)(ping)方千米，是(shi)四川(chuan)盆地最大(da)的平(ping)(ping)原(yuan)(yuan)，也是(shi)西(xi)南地區最大(da)的平(ping)(ping)原(yuan)(yuan)，海拔約600米。
四川(chuan)(chuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)屬揚(yang)子(zi)準地(di)(di)(di)(di)(di)(di)(di)(di)(di)臺(tai)四川(chuan)(chuan)臺(tai)坳。古生(sheng)代(dai)時相(xiang)(xiang)對(dui)隆(long)起，缺(que)乏泥(ni)(ni)盆(pen)(pen)(pen)系(xi)(xi)和(he)(he)石(shi)炭系(xi)(xi)。印(yin)支運動(dong)轉換為(wei)(wei)(wei)大(da)型(xing)拗陷(xian)，晚燕山(shan)(shan)(shan)運動(dong)，特別是(shi)喜馬拉(la)雅運動(dong)后發生(sheng)褶皺隆(long)起。盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)的(de)(de)(de)(de)格局(ju)主(zhu)要(yao)受北東(dong)—南西向及(ji)北西向兩(liang)(liang)條(tiao)構(gou)造(zao)線(xian)控制(zhi)，構(gou)成(cheng)(cheng)了典型(xing)的(de)(de)(de)(de)菱形盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)，四川(chuan)(chuan)廣(guang)元、四川(chuan)(chuan)雅安、四川(chuan)(chuan)敘永為(wei)(wei)(wei)菱形的(de)(de)(de)(de)四頂點(dian)，東(dong)西兩(liang)(liang)邊(bian)稍長，為(wei)(wei)(wei)380～430公(gong)(gong)里，南北兩(liang)(liang)邊(bian)略短(duan)，為(wei)(wei)(wei)310～330公(gong)(gong)里。以上菱形四頂點(dian)的(de)(de)(de)(de)連線(xian)與(yu)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)內(nei)650～750米(mi)的(de)(de)(de)(de)等高線(xian)大(da)體相(xiang)(xiang)當，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)底部(bu)與(yu)邊(bian)緣(yuan)山(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)也以此為(wei)(wei)(wei)分界。四川(chuan)(chuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)在(zai)距(ju)今1.4億年(nian)以前(qian)，還是(shi)內(nei)陸(lu)湖盆(pen)(pen)(pen)。至(zhi)距(ju)今6.6千(qian)萬年(nian)時，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)邊(bian)緣(yuan)山(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)迅速(su)隆(long)升，長江中(zhong)(zhong)上游水系(xi)(xi)開始溝通。盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)內(nei)湖水東(dong)瀉奠定了現今之(zhi)地(di)(di)(di)(di)(di)(di)(di)(di)(di)貌形態。盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)邊(bian)緣(yuan)多(duo)(duo)低山(shan)(shan)(shan)和(he)(he)中(zhong)(zhong)山(shan)(shan)(shan)，山(shan)(shan)(shan)勢陡峻，發源(yuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)邊(bian)緣(yuan)山(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)的(de)(de)(de)(de)河(he)流大(da)多(duo)(duo)為(wei)(wei)(wei)“V”型(xing)谷(gu)，嶺(ling)谷(gu)高差都(dou)逾500～1 000米(mi)， 地(di)(di)(di)(di)(di)(di)(di)(di)(di)表(biao)崎(qi)嶇，故(gu)歷(li)史上就(jiu)有“蜀道(dao)難(nan)，難(nan)于上青(qing)天(tian)”之(zhi)說。山(shan)(shan)(shan)脊海(hai)拔大(da)多(duo)(duo)在(zai)2000～3000米(mi)，西北部(bu)與(yu)西部(bu)可超過3000～4000米(mi)，如(ru)龍門山(shan)(shan)(shan)4984米(mi)，峨眉山(shan)(shan)(shan)3099米(mi)，小相(xiang)(xiang)嶺(ling)4 791米(mi)。地(di)(di)(di)(di)(di)(di)(di)(di)(di)表(biao)廣(guang)泛出露古生(sheng)代(dai)及(ji)其以前(qian)的(de)(de)(de)(de)石(shi)灰巖(yan)，其次(ci)為(wei)(wei)(wei)板巖(yan)、片巖(yan)、結晶灰巖(yan)、石(shi)英巖(yan)、砂泥(ni)(ni)巖(yan)和(he)(he)礫巖(yan)，局(ju)部(bu)有花崗巖(yan)和(he)(he)玄武巖(yan)。石(shi)灰巖(yan)分布區(qu)可見(jian)石(shi)林、溶(rong)洞、暗(an)河(he)、槽谷(gu)等喀斯特地(di)(di)(di)(di)(di)(di)(di)(di)(di)貌，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)南緣(yuan)興(xing)文縣(xian)素(su)有“石(shi)林洞鄉”之(zhi)稱（見(jian)興(xing)文石(shi)林）。巫(wu)山(shan)(shan)(shan)十二峰和(he)(he)金(jin)佛山(shan)(shan)(shan)等名(ming)山(shan)(shan)(shan)主(zhu)要(yao)也由(you)(you)石(shi)灰巖(yan)發育而成(cheng)(cheng)。由(you)(you)石(shi)灰巖(yan)、玄武巖(yan)、花崗巖(yan)等組成(cheng)(cheng)的(de)(de)(de)(de)峨眉山(shan)(shan)(shan)及(ji)由(you)(you)砂泥(ni)(ni)巖(yan)、礫巖(yan)組成(cheng)(cheng)的(de)(de)(de)(de)青(qing)城山(shan)(shan)(shan)，素(su)有“峨眉天(tian)下秀”、“青(qing)城天(tian)下幽”之(zhi)稱，為(wei)(wei)(wei)中(zhong)(zhong)國著名(ming)游覽勝地(di)(di)(di)(di)(di)(di)(di)(di)(di)。盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)底部(bu)海(hai)拔多(duo)(duo)數在(zai)250～700米(mi)，地(di)(di)(di)(di)(di)(di)(di)(di)(di)勢東(dong)南傾，盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)內(nei)各河(he)流均由(you)(you)邊(bian)緣(yuan)山(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)(di)(di)(di)匯聚盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)底部(bu)的(de)(de)(de)(de)長江干流，形成(cheng)(cheng)向心狀水系(xi)(xi)。地(di)(di)(di)(di)(di)(di)(di)(di)(di)表(biao)為(wei)(wei)(wei)大(da)面積(ji)的(de)(de)(de)(de)中(zhong)(zhong)生(sheng)代(dai)紫紅色砂巖(yan)與(yu)泥(ni)(ni)巖(yan)所覆(fu)蓋，故(gu)稱為(wei)(wei)(wei)“紅層盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)”，是(shi)中(zhong)(zhong)國中(zhong)(zhong)生(sheng)代(dai)陸(lu)相(xiang)(xiang)紅層分布最集中(zhong)(zhong)地(di)(di)(di)(di)(di)(di)(di)(di)(di)區(qu)。四川(chuan)(chuan)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)為(wei)(wei)(wei)丘陵性(xing)盆(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)(di)(di)(di)，底部(bu)以丘陵為(wei)(wei)(wei)主(zhu)，次(ci)為(wei)(wei)(wei)低山(shan)(shan)(shan)和(he)(he)平原。
四川盆地(di)(di)屬(shu)揚子(zi)陸(lu)臺一(yi)部分，稱為四川陸(lu)臺，屬(shu)較穩定的地(di)(di)區，但(dan)仍經(jing)過兩次(ci)大(da)規模的海(hai)(hai)浸(jin)。第(di)一(yi)次(ci)從5億(yi)多年(nian)前的寒武(wu)紀(ji)開始，延續(xu)到3.7億(yi)多年(nian)的志留紀(ji)，不斷下陷成了海(hai)(hai)洋盆地(di)(di)，志留紀(ji)時發生加里東運動，除了西部的龍(long)門山地(di)(di)槽(cao)繼續(xu)下陷外(wai)，其余地(di)(di)區上升為陸(lu)。2.7億(yi)年(nian)前的石炭紀(ji)末，發生范圍(wei)更大(da)的第(di)二次(ci)海(hai)(hai)浸(jin)，盆地(di)(di)再次(ci)為海(hai)(hai)洋占據。二疊(die)(die)紀(ji)時海(hai)(hai)陸(lu)交替，形成重(zhong)慶(qing)附近(jin)的南酮、松藻、天(tian)府等(deng)煤礦。二疊(die)(die)紀(ji)末，盆地(di)(di)西部巖漿(jiang)噴出，峨(e)眉山小金頂及(ji)清(qing)音閣(ge)一(yi)帶(dai)的玄武(wu)巖就在這時生成。
距今(jin)1.9億年的(de)三疊(die)紀，“印(yin)支運動”使盆(pen)(pen)地(di)(di)邊(bian)緣(yuan)逐漸隆起成山，被(bei)海水淹沒(mei)的(de)地(di)(di)區逐漸上升成陸，由(you)海盆(pen)(pen)轉為湖盆(pen)(pen)。當時湖水幾乎占據現今(jin)四川盆(pen)(pen)地(di)(di)的(de)全境，稱為“蜀(shu)湖”，從此結束(shu)了海浸(jin)的(de)歷史。在中生代漫(man)長的(de)1億多(duo)年里(li)，盆(pen)(pen)地(di)(di)氣候溫暖濕潤，到處(chu)生長蕨類、蘇鐵(tie)和裸(luo)子植物(wu)，是又一(yi)個(ge)成煤期，永榮(rong)煤礦即在三疊(die)紀和侏羅(luo)紀時形成。東(dong)起長壽、墊(dian)江，西(xi)到江油、邛崍，北抵大(da)巴山麓(lu)，南到貴州赤水，還(huan)是天然氣富集(ji)區。這一(yi)時期爬行動物(wu)恐(kong)龍稱霸一(yi)時。1957年在合(he)州發現的(de)“合(he)州馬(ma)門溪龍”身長22米，高3.5米，是中國亞洲最大(da)和最完整的(de)恐(kong)龍化石。
7000萬年前的(de)(de)(de)(de)(de)(de)白堊紀末期，發生(sheng)又一次強烈的(de)(de)(de)(de)(de)(de)地(di)(di)(di)(di)殼運(yun)(yun)動(dong)“燕(yan)山(shan)運(yun)(yun)動(dong)”。盆(pen)地(di)(di)(di)(di)四(si)周山(shan)地(di)(di)(di)(di)繼續隆(long)起，同時產生(sheng)不(bu)少大(da)斷層(ceng)，如西部(bu)(bu)的(de)(de)(de)(de)(de)(de)龍(long)門(men)山(shan)大(da)斷層(ceng)和東(dong)部(bu)(bu)的(de)(de)(de)(de)(de)(de)華瑩山(shan)大(da)斷層(ceng)，把盆(pen)地(di)(di)(di)(di)分(fen)為三部(bu)(bu)分(fen)。蜀湖縮(suo)小為僅有2萬平方公(gong)里的(de)(de)(de)(de)(de)(de)蜀湖。封(feng)閉的(de)(de)(de)(de)(de)(de)盆(pen)地(di)(di)(di)(di)地(di)(di)(di)(di)形及(ji)急劇(ju)縮(suo)小的(de)(de)(de)(de)(de)(de)水(shui)面，使氣(qi)候逐漸變(bian)得(de)干(gan)熱，沉積物由海相(xiang)、海陸交替相(xiang)變(bian)為陸相(xiang)，大(da)量(liang)風化、侵(qin)蝕(shi)(shi)、剝蝕(shi)(shi)的(de)(de)(de)(de)(de)(de)物質在(zai)盆(pen)地(di)(di)(di)(di)堆(dui)積了數千米(mi)厚，形成紅(hong)色(se)和紫紅(hong)色(se)的(de)(de)(de)(de)(de)(de)砂、泥(ni)(ni)、頁巖。裸(luo)子植(zhi)物不(bu)斷衰(shuai)退(tui)，恐龍(long)滅(mie)絕了。內(nei)陸湖泊在(zai)干(gan)燥條件下，經(jing)強烈蒸發，濃度增(zeng)大(da)，鹽分(fen)不(bu)斷積累，形成鹽湖，后來泥(ni)(ni)沙掩埋而保存于地(di)(di)(di)(di)層(ceng)之(zhi)中(zhong)(zhong)，經(jing)過漫(man)長的(de)(de)(de)(de)(de)(de)地(di)(di)(di)(di)質作用(yong)形成巖層(ceng)，自貢一帶(dai)是(shi)著名(ming)的(de)(de)(de)(de)(de)(de)井鹽產地(di)(di)(di)(di)。 2000多萬年前的(de)(de)(de)(de)(de)(de)新第三紀，受喜馬(ma)拉雅造(zao)山(shan)運(yun)(yun)動(dong)的(de)(de)(de)(de)(de)(de)影(ying)響。距(ju)今二、三百萬年的(de)(de)(de)(de)(de)(de)第四(si)紀，地(di)(di)(di)(di)殼再次發生(sheng)構造(zao)運(yun)(yun)動(dong)。從(cong)而，四(si)川盆(pen)地(di)(di)(di)(di)由內(nei)流(liu)(liu)盆(pen)地(di)(di)(di)(di)變(bian)為外流(liu)(liu)陸盆(pen)，由封(feng)閉的(de)(de)(de)(de)(de)(de)內(nei)流(liu)(liu)區(qu)變(bian)為外流(liu)(liu)區(qu)，由以堆(dui)積為主(zhu)變(bian)為侵(qin)蝕(shi)(shi)為主(zhu)，經(jing)歷了海盆(pen)——湖盆(pen)——陸盆(pen)的(de)(de)(de)(de)(de)(de)滄(cang)桑之(zhi)變(bian)。 第四(si)紀是(shi)冰(bing)川廣(guang)布的(de)(de)(de)(de)(de)(de)時代，盆(pen)地(di)(di)(di)(di)西北山(shan)地(di)(di)(di)(di)發育大(da)量(liang)冰(bing)川。冰(bing)川消融后，大(da)量(liang)沉積物由岷江、沱江等攜(xie)帶(dai)，堆(dui)積在(zai)西部(bu)(bu)的(de)(de)(de)(de)(de)(de)凹陷區(qu)，即以前的(de)(de)(de)(de)(de)(de)蜀湖之(zhi)中(zhong)(zhong)，最終形成了成都(dou)平原。 四(si)川盆(pen)地(di)(di)(di)(di)地(di)(di)(di)(di)貌豐富，平原7%，丘陵52%，低山(shan)41%。
四川(chuan)盆(pen)地(di)中植(zhi)物(wu)近(jin)萬(wan)種，古老而特(te)有(you)種之多為中國其他(ta)地(di)區所(suo)不及。在盆(pen)地(di)邊緣山地(di)及盆(pen)東平(ping)行嶺(ling)谷(gu)尚可(ke)見(jian)水杉(shan)、銀杉(shan)、鵝掌楸、檫木(mu)(mu)、三尖(jian)杉(shan)、珙桐、水青樹、連香(xiang)樹、領春木(mu)(mu)、金錢(qian)槭、蠟梅、杜仲、紅(hong)豆杉(shan)、鐘萼木(mu)(mu)、福建柏、穗(sui)花杉(shan)、崖柏、木(mu)(mu)瓜紅(hong)等珍稀孑遺植(zhi)物(wu)與(yu)特(te)有(you)種。在濕熱(re)河谷(gu)可(ke)見(jian)桫欏(luo)、小羽桫欏(luo)、烏毛蕨、華(hua)(hua)南紫萁(ji)、里白(bai)等古熱(re)帶(dai)(dai)孑遺植(zhi)物(wu)。 四川(chuan)盆(pen)地(di)的地(di)帶(dai)(dai)性(xing)植(zhi)被是亞熱(re)帶(dai)(dai)常綠闊(kuo)葉(xie)(xie)(xie)(xie)(xie)林，其代表樹種有(you)栲樹、峨(e)眉栲、刺果米櫧、青岡、曼青岡、包(bao)石櫟(li)、華(hua)(hua)木(mu)(mu)荷、大包(bao)木(mu)(mu)荷、四川(chuan)大頭茶、楨楠、潤楠等，海拔(ba)一般情(qing)況(kuang)下(xia)在1600～1 800米以下(xia)。其次有(you)馬尾松、杉(shan)木(mu)(mu)、柏木(mu)(mu)組成 的亞熱(re)帶(dai)(dai)針葉(xie)(xie)(xie)(xie)(xie)林及竹林。 邊緣山地(di)從下(xia)而上是常綠闊(kuo)葉(xie)(xie)(xie)(xie)(xie)林、常綠闊(kuo)葉(xie)(xie)(xie)(xie)(xie)與(yu)落(luo)葉(xie)(xie)(xie)(xie)(xie)闊(kuo)葉(xie)(xie)(xie)(xie)(xie)混交林，寒溫帶(dai)(dai)山地(di)針葉(xie)(xie)(xie)(xie)(xie)林，局部(bu)有(you)亞高山灌叢草甸(dian)。
四(si)川(chuan)(chuan)盆地(di)(di)是(shi)中(zhong)(zhong)國動(dong)(dong)物(wu)(wu)種類(lei)最(zui)多、最(zui)齊全的(de)地(di)(di)區之一。據統計(ji)，除魚類(lei)外，盆地(di)(di)底部共有(you)(you)動(dong)(dong)物(wu)(wu)417種，盆地(di)(di)西緣(yuan)(yuan)、北(bei)緣(yuan)(yuan)和南緣(yuan)(yuan)山地(di)(di)分(fen)別為487種、317種與288種，其中(zhong)(zhong)經濟(ji)動(dong)(dong)物(wu)(wu)均(jun)占(zhan)一半以(yi)上。盆地(di)(di)西緣(yuan)(yuan)山地(di)(di)是(shi)中(zhong)(zhong)國特(te)有(you)(you)而古老動(dong)(dong)物(wu)(wu)保存最(zui)好(hao)、最(zui)集(ji)中(zhong)(zhong)的(de)地(di)(di)區，屬于(yu)一類(lei)保護(hu)(hu)動(dong)(dong)物(wu)(wu)的(de)有(you)(you)大熊(xiong)貓(mao)(mao)、金絲猴(hou)(hou)、扭角羚、灰金絲猴(hou)(hou)、白唇鹿等(deng)。還有(you)(you)珍貴特(te)有(you)(you)動(dong)(dong)物(wu)(wu)小熊(xiong)貓(mao)(mao)、雪豹(bao)、鬣羚、短(duan)尾猴(hou)(hou)、獼猴(hou)(hou)、毛冠鹿、水獺及鴛鴦(yang)、血雉(zhi)、紅(hong)腹角雉(zhi)、綠尾虹雉(zhi)、白腹錦(jin)雞、紅(hong)腹錦(jin)雞等(deng)。 盆地(di)(di)西緣(yuan)(yuan)的(de)平武、青川(chuan)(chuan)、北(bei)川(chuan)(chuan)、寶興、天全、洪(hong)雅、馬邊(bian)(bian)等(deng)地(di)(di)，均(jun)為中(zhong)(zhong)國大熊(xiong)貓(mao)(mao)的(de)主要(yao)分(fen)布區。已設立(li)唐家河(he)、王朗、臥(wo)龍(long)（見(jian)臥(wo)龍(long)自然(ran)保護(hu)(hu)區）、蜂桶寨、喇叭河(he)等(deng)7處大熊(xiong)貓(mao)(mao)、金絲猴(hou)(hou)等(deng)自然(ran)保護(hu)(hu)區。 酉陽(yang)、馬邊(bian)(bian)、平武等(deng)盆地(di)(di)邊(bian)(bian)緣(yuan)(yuan)山地(di)(di)溪溝中(zhong)(zhong)的(de)大鯢及長(chang)江、金沙江中(zhong)(zhong)的(de)中(zhong)(zhong)華(hua)鱘、白鱘也(ye)為四(si)川(chuan)(chuan)所特(te)有(you)(you)，均(jun)屬國家保護(hu)(hu)動(dong)(dong)物(wu)(wu)。
四(si)川(chuan)盆地(di)有煤(mei)、鐵(tie)、天(tian)然氣(qi)、石(shi)(shi)油、鹽、芒(mang)硝(xiao)、石(shi)(shi)膏(gao)、磷、硫、鋁、金、銅、錳、石(shi)(shi)墨(mo)、汞(gong)等(deng)(deng)礦(kuang)產(chan)資源，其中(zhong)(zhong)天(tian)然氣(qi)、芒(mang)硝(xiao)為全中(zhong)(zhong)國(guo)之(zhi)冠，并有中(zhong)(zhong)國(guo)重要的鍶礦(kuang)。川(chuan)東北是世界最大的天(tian)然氣(qi)富集區之(zhi)一，川(chuan)中(zhong)(zhong)和(he)南(nan)充等(deng)(deng)地(di)鹽巖礦(kuang)儲(chu)量(liang)很(hen)大。
四川(chuan)盆(pen)(pen)(pen)地(di)(di)(di)地(di)(di)(di)形閉(bi)塞(sai)，由于(yu)(yu)(yu)北部(bu)秦嶺阻擋冷(leng)空氣，冬季氣溫高(gao)于(yu)(yu)(yu)同(tong)緯(wei)度(du)(du)其他(ta)地(di)(di)(di)區。最冷(leng)月北部(bu)均(jun)(jun)溫3～5℃，南(nan)部(bu)5~8℃，較同(tong)緯(wei)度(du)(du)的(de)(de)上(shang)海(hai)、湖(hu)北、安(an)徽及緯(wei)度(du)(du)偏(pian)南(nan)的(de)(de)貴州高(gao)1～4℃。盆(pen)(pen)(pen)地(di)(di)(di)北部(bu)極端(duan)最低(di)溫-8～-5℃，南(nan)部(bu)-5℃~-2℃。霜雪少(shao)見，年無(wu)(wu)霜期長280～350天，同(tong)緯(wei)度(du)(du)上(shang)的(de)(de)武漢冬天卻霜雪不(bu)斷(duan)，盆(pen)(pen)(pen)地(di)(di)(di)位于(yu)(yu)(yu)長江河谷中的(de)(de)長寧全年無(wu)(wu)霜。 盆(pen)(pen)(pen)地(di)(di)(di)各地(di)(di)(di)夏(xia)季始于(yu)(yu)(yu)5月底，終(zhong)于(yu)(yu)(yu)9月中旬，夏(xia)長4個月，溫度(du)(du)上(shang)東高(gao)西(xi)低(di)。盆(pen)(pen)(pen)地(di)(di)(di)西(xi)部(bu)夏(xia)天平均(jun)(jun)氣溫約25℃，較同(tong)緯(wei)度(du)(du)的(de)(de)上(shang)海(hai)、武漢等城市偏(pian)低(di)3-4度(du)(du)，但濕度(du)(du)較大，所(suo)以(yi)悶熱難忍。
東部(bu)最熱(re)月氣(qi)(qi)(qi)(qi)溫(wen)(wen)(wen)(wen)高(gao)達26～29℃，長(chang)(chang)江河谷局地(di)(di)(di)達到30℃。盛(sheng)夏(xia)連(lian)晴高(gao)溫(wen)(wen)(wen)(wen)天氣(qi)(qi)(qi)(qi)又造成盆(pen)(pen)地(di)(di)(di)東南(nan)部(bu)嚴重(zhong)的(de)夏(xia)伏旱(han)。盆(pen)(pen)地(di)(di)(di)氣(qi)(qi)(qi)(qi)溫(wen)(wen)(wen)(wen)東南(nan)高(gao)西北(bei)低，盆(pen)(pen)底高(gao)邊(bian)緣(yuan)低； 各(ge)地(di)(di)(di)年均(jun)溫(wen)(wen)(wen)(wen)16～18℃。10℃以(yi)上活(huo)(huo)動(dong)積(ji)溫(wen)(wen)(wen)(wen)4500～6000℃，持續期8～9個月，屬中(zhong)(zhong)亞熱(re)帶(dai)。東南(nan)部(bu)的(de)長(chang)(chang)江河谷積(ji)溫(wen)(wen)(wen)(wen)超(chao)過6000℃，相當于中(zhong)(zhong)國南(nan)嶺以(yi)南(nan)的(de)南(nan)亞熱(re)帶(dai)氣(qi)(qi)(qi)(qi)候。盆(pen)(pen)地(di)(di)(di)氣(qi)(qi)(qi)(qi)溫(wen)(wen)(wen)(wen)東高(gao)西低，南(nan)高(gao)北(bei)低，盆(pen)(pen)底高(gao)而邊(bian)緣(yuan)低，等溫(wen)(wen)(wen)(wen)線分(fen)布(bu)(bu)呈現同心圓狀。盆(pen)(pen)地(di)(di)(di)邊(bian)緣(yuan)山地(di)(di)(di)氣(qi)(qi)(qi)(qi)溫(wen)(wen)(wen)(wen)具(ju)有垂直(zhi)分(fen)布(bu)(bu)特(te)點，如峨眉山、金(jin)佛(fo)山海(hai)拔升高(gao)百(bai)米，氣(qi)(qi)(qi)(qi)溫(wen)(wen)(wen)(wen)遞減0.55℃和(he)0.61℃。峨眉山頂年均(jun)溫(wen)(wen)(wen)(wen)僅3℃，10℃以(yi)上活(huo)(huo)動(dong)積(ji)溫(wen)(wen)(wen)(wen)586℃，氣(qi)(qi)(qi)(qi)候上相當于寒溫(wen)(wen)(wen)(wen)帶(dai)和(he)亞寒帶(dai)。
四川(chuan)盆地(di)(di)年(nian)(nian)降水量(liang)(liang)1000～1300毫(hao)(hao)米，盆地(di)(di)邊緣山(shan)(shan)(shan)地(di)(di)降水十分充沛(pei)，如樂山(shan)(shan)(shan)和雅安間的西(xi)緣山(shan)(shan)(shan)地(di)(di)年(nian)(nian)降水量(liang)(liang)為(wei)1 500～1800毫(hao)(hao)米，為(wei)中(zhong)國(guo)突(tu)出的多(duo)雨區(qu)(qu)，有“華(hua)西(xi)雨屏(ping)”之稱。但(dan)冬干、春旱(han)、夏澇、秋綿雨，年(nian)(nian)內分配不均(jun)，70～75%的雨量(liang)(liang)集中(zhong)于6～10月(yue)。最(zui)大日(ri)降水量(liang)(liang)可達300～500毫(hao)(hao)米。“巴山(shan)(shan)(shan)夜雨”自(zi)古聞名(ming)，夜雨占總雨量(liang)(liang)的60～70%以(yi)上。盆地(di)(di)區(qu)(qu)霧大濕重，云低陰天多(duo)。峨(e)眉山(shan)(shan)(shan)、金佛山(shan)(shan)(shan)是中(zhong)國(guo)霧日(ri)最(zui)多(duo)地(di)(di)區(qu)(qu)之一，年(nian)(nian)相對濕度(du)之高也為(wei)中(zhong)國(guo)之冠(guan)。盆地(di)(di)年(nian)(nian)日(ri)照(zhao)僅900～1300小時(shi)，年(nian)(nian)太(tai)陽(yang)輻射量(liang)(liang)為(wei)370～420千焦耳/平方(fang)厘米，均(jun)為(wei)中(zhong)國(guo)最(zui)低值，故有“蜀犬吠(fei)日(ri)”之說。
